How sustainable and profitable are large-scale hydrogen production plants from CH₄ and H₂S?

The large-scale production of hydrogen through mature technologies such as steam methane reforming (SMR) has set a benchmark for emerging hydrogen production processes to gauge their economic viability for the hydrogen economy. In this work, we use detailed process modeling to perform a techno-economic and environmental assessments on the potential of alternative emerging hydrogen production processes based on H₂S utilization including H₂S-methane reforming (H₂SMR), and H₂S pyrolysis (H₂SPyrol) compared to steam methane reforming (SMR), SMR with CO₂ capture, storage, and utilization (CCUS), and CH₄ pyrolysis (CH₄Pyrol). Technically, the energy intensity of these processes in terms of electrical and thermal energy consumption was ranked as CH₄Pyrol < SMR < SMR + CCUS < H₂SMR < H₂SPyrol. However, lower CH₄ feedstock and absence of direct CO₂ emissions were seen for H₂SMR for the same target hydrogen production. Economically, both H₂S-based hydrogen production technologies were competitive with levelized cost of hydrogen (LCOH) of $-1.000 and $3.537 per kg for H₂SMR and H₂SPyrol, respectively, compared to LCOH of $2.400, $2.410, and $1.930 per kg for SMR, SMR + CCUS, and CH₄Pyrol, respectively, with consideration for by-product sales, and sensitivity analysis to their market prices and effect of carbon taxes. Environmentally, H₂SMR and H₂SPyrol revealed their lower contribution to global warming, with the absence of direct CO₂ emissions, qualifying as low carbon hydrogen production processes. Although direct CO₂ emissions are missing from CH₄Pyrol, its qualification as low carbon hydrogen producer hinges on the level of decarbonization for the electricity grid. Conversely, the water footprint of H₂S-based hydrogen production process remains to be the largest due to the indirect consumption of cooling water required for product recovery, although not necessarily impacting water stress, due to the lower quality of water required for cooling. In summary, transitioning from SMR wo/w CCUS to H₂SMR or CH₄Pyrol seems to be potentially attractive for competing with current processes for H₂ production within the existing policies for decarbonization.